Grout bag type of underground support

ABSTRACT

A grout bag assembly ( 1 ) is provided comprising an inflatable grout bag ( 2 ) (hereinafter termed a primary inflatable grout bag) having a top ( 4 ), bottom ( 6 ) and at least one side ( 8 ) and having in an expanded condition an axis extending between the top and bottom thereof. A secondary, independently inflatable, grout bag ( 14 ) expandable in the same direction as the primary inflatable bag is attached to one end of the primary inflatable grout bag. The secondary grout bag is employed, in use, subsequent to be installation of the primary grout bag to compensate for shrinkage in the height of the primary grout bag and to thereby supplement the overall axial dimension of the grout bag assembly, in use.

FIELD OF THE INVENTION

This invention relates to a grout bag type of underground support for use in underground mining operations in order to support the roof or hanging wall. More particularly, the invention relates to an underground support in the general form of a grout bag used for containing granular material that may be set solid using cementitious or other suitable binding material to form a so-called grout pack.

In this specification the term “grout bag” is intended to have its widest meaning and to include any appropriate enclosure made of a flexible material for the purpose of containing granular, including solidified granular, material serving as a mine roof or hanging wall support, in use.

BACKGROUND TO THE INVENTION

The support of the hanging wall in stopes is one of the most basic requirements in underground mining operations. Dependant on the type and quality of rock being supported, the depth of mining, the prevalent field stresses, seismicity, stoping width and a number of other factors, underground mine roof support can vary across a vast range of materials, configurations and systems. These include, amongst others, timber poles, timber and composite packs, steel props, unmined ore pillars, rock anchors and granular or tailings type supports.

Among granular support media, cemented grout packs are increasingly being used as combination support products. These consist essentially of a support column formed by cured cemented backfill or other suitable cured cementitious grout which is contained within a geotextile bag and generally stiffened with external restraining rings or metal mesh against lateral deformation or bulging during installation and under subsequent axial load.

Conventional grout bags are essentially closed geotextile containers, typically made of woven ribbons and monofilaments of polyethylene and polypropylene to have required filtering characteristics to retain solid particles whilst allowing excess liquid to escape. The bag has some form of unidirectional valve for inflating the bags slurry under pressure. The bags also typically have some means of suspending them on support structures within the stopes using ties or loops to facilitate their installation.

Once the bags have been inflated with slurry, typically as a grout, the material needs to cure or set to develop sufficient strength to carry load. The curing process usually involves the bonding and/or percolation loss of water resulting in volumetric shrinkage of the grout. Due to gravitational sag, such shrinkage usually results in at the least vertical shrinkage and loss of hanging wall contact. This in turn results in the support not providing immediate effective hanging wall support.

To counteract the loss of hanging wall contact through such shrinkage, grout packs are often post-stressed by means of separate, secondary grout bags of appreciably lesser height which are installed between the top of the shrunken grout pack and the hanging wall. It is, however, often difficult to correctly position the secondary bag and to maintain it in position during filling.

It is also logistically inconvenient to transport and store such separate items with the result that secondary grout bags are frequently not available where needed and may be over supplied in other areas. Not only is this inconvenient and wasteful but it also can lead to dangerous situations arising where the hanging wall is not adequately supported or not supported as soon as it may otherwise have been.

OBJECT OF THE INVENTION

It is an object of this invention to provide an underground support of the general nature of an inflatable bag which will, at least partially, alleviate one or more of the abovementioned problems.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a grout bag assembly comprising an inflatable grout bag (hereinafter termed a primary inflatable grout bag) having a top, bottom and at least one side and having in an expanded condition an axis extending between the top and bottom thereof, the grout bag assembly being characterised in that the primary inflatable grout bag has attached thereto, at either the top or bottom thereof in the axial direction, a secondary, independently inflatable grout bag expandable in the same direction as the primary inflatable bag to supplement the overall axial dimension of the grout bag assembly, in use.

Further features of the invention provide for the secondary grout bag to be of the same general shape in plan view as the primary grout bag with a substantially smaller maximum distance between the top and bottom thereof relative to the maximum distance between the top and bottom of the primary grout bag; for the said maximum distance in the instance of the secondary grout bag to be from about 100 to about 250 millimetres whereas the maximum dimensioned of the primary inflatable grout bag is from about 600 mm to about 1500 mm; for the secondary grout bag to be located on the top of the primary grout bag; and for the top of the primary grout bag and the bottom of the secondary grout bag to be formed by a single common wall.

Still further features of the invention provide for each of the primary grout bag and secondary grout bag to have a unidirectional valve-controlled inlet; and for the primary grout bag and secondary grout bag to be located within a further outer bag.

A yet further feature of the invention provides for a reinforcing structure in the form of external restraining rings or metal or other mesh to be provided about at least the primary grout bag, preferably about both the primary grout bag and the secondary grout bag.

In order that the invention may be more fully understood an embodiment thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective schematic view of one embodiment of grout bag assembly according to the invention;

FIG. 2 is a schematic sectional side elevation thereof;

FIGS. 3 a to 3 d are schematic side elevations of the grout bag assembly illustrated in FIGS. 1 and 2 in various progressive stages of installation thereof; and,

FIG. 4 is a sectional side elevation of a modified embodiment of an underground support.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In the embodiment of the invention illustrated in FIGS. 1 and 2, a grout bag assembly (1) includes a primary inflatable grout bag (2) made of a geotextile material and having a cylindrical shape with a top (4), bottom (6) and side (8). A unidirectional valve-controlled inlet (10) is provided in the side (8) near the top (4) in conventional fashion. The unidirectional valve is, in this embodiment, simply formed by a tube made of a flexible material which extends internally of the primary grout bag (2) and which is collapsed in its normal condition. Such valves are well known.

The general construction of the grout bags and the materials used may be the same as those used currently for existing grout bags and the details need not be further described herein. The maximum height of such a bag taken along its axis “A” will depend on the height of the hanging wall to be supported and is typically in the range of about 800 mm to 1500 mm.

As provided by this invention, a secondary inflatable grout bag (14) of substantially lesser maximum axial height than the primary grout bag, extends from the top (4) of the primary grout bag (2). The secondary grout bag (14) has a cylindrical shape that is the same, in plan view, as the primary grout bag, with a top (16), bottom (18) and side (20). The maximum height of the secondary grout bag will typically be about 100 to about 250 mm, depending at least to some extent on the overall height of the primary grout bag and the height of the hanging wall to be supported.

In this embodiment of the invention, the side (20) of the secondary bag is either integral with, or attached directly to, the side of the primary bag (2) to effectively form an extension thereto. Thus, the bottom (18) of the secondary grout bag is formed by the top (4) of the primary grout bag.

The secondary grout bag also has a unidirectional valve-controlled inlet (22) in its side (20) adjacent the top (16) thereof. Fabric ties (24) are spaced about the periphery of the top (16) of the secondary grout bag (14).

Installation of the grout bag assembly (1) is shown in use in FIGS. 3 a to 3 d. Initially, the grout bag assembly (1) is positioned between a hanging wall (30) and a foot wall (32) of a mine with the bottom (6) of the primary grout bag (2) on the foot wall (32) in the usual way.

The primary grout bag (2) is preferably suspended from its top (4) by a reinforcing cage (not shown) located about the primary grout bag (2) or from the hanging wall (30) in the general orientation shown in FIG. 3 a. Hereafter, the primary grout bag (2) is inflated/filled by pumping a slurry (34), in this embodiment a cementitious grout, into it through the unidirectional valve-controlled inlet (10) in conventional fashion.

This causes expansion of the primary bag both laterally and in the direction of the axis between the top (4) and bottom (6) thereof. Filling continues until the secondary bag (14) becomes compressed between the primary bag (2) and hanging wall (30). Hereafter the grout (34) is allowed to set.

As shown in FIG. 3 c, once the grout (34) has set, axial shrinkage of the primary grout bag (2) occurs. This results in a loss of compressive load from the hanging wall (30) on the primary grout bag (2).

Once the grout (34) has fully cured, the secondary bag (14) is filled with grout (36) through its unidirectional valve-controlled inlet (22) as shown in FIG. 3 d. The grout (36) can be the same as that used to fill the primary grout bag (2) or it could be different, for example, it may be selected to have a lower degree of shrinkage than in the instance of the slurry used to fill the primary grout bag. Filling of the secondary bag (14) continues until the top (16) engages the hanging wall (30) and the required internal pressure is reached within the secondary grout bag (14). Hereafter, the grout (36) is allowed to set.

Although there will typically be shrinkage of the grout in the secondary bag (14) this will not be as significant as that of the grout in the primary bag (2) due to the substantially smaller height of the secondary bag (14).

The underground support provided by this invention thus allows fast and convenient post-stressing of the primary bag without the need for additional separate bags or other post-stressing devices. The secondary bag remains ideally positioned on top of the primary bag at all times and it is thus not possible to misalign it.

The elimination of time required to transport and locate a secondary separate bag in position not only results in operational efficiencies but also in greater worker safety as the time spent working in unsupported environments is reduced.

The grout bag assembly can typically also be more cheaply manufactured than separate grout bags and post-stressing bags. Inventory control as well as transport and storage are also greatly facilitated.

It will be appreciated that many other embodiments of grout bag assembly exist which fall within the scope of the invention particularly as regards the shape and configuration thereof and the materials used in the construction thereof.

For example, as shown in FIG. 4, the grout bag assembly (40) could be provided with an outer bag (42) within which a separate primary grout bag (44) and a separate secondary grout bag (46) are located. Also, each or either of the primary bag and secondary bag could have an internal bladder and different materials could be used in the construction of each of the primary bag and secondary bag. This may, for example, be desirable where it is desired to fill each with a different material offering different setting characteristics.

Any suitable lateral support could be provided about either or both the primary bag and secondary bag. 

1. A grout bag assembly comprising a primary inflatable grout bag having a top, bottom and at least one side and having in an expanded condition an axis extending between the top and bottom thereof, wherein the primary inflatable grout bag has attached thereto, at either the top or bottom thereof in the axial direction, a secondary, independently inflatable grout bag having a top and a bottom and expandable in the same direction as the primary inflatable bag to supplement the overall axial dimension of the grout bag assembly, in use, wherein the secondary grout bag has a substantially smaller maximum distance between the top and bottom thereof in an expanded condition relative to the maximum distance between the top and bottom of the primary grout bag in an expanded condition.
 2. A grout bag assembly as claimed in claim 1 in which the secondary grout bag is of the same general shape in plan view as the primary grout bag.
 3. A grout bag assembly as claimed in claim 1 in which the said maximum distance in the instance of the secondary grout bag is from about 100 mm (4 inches) to about 250 mm (10 inches) whereas the maximum distance in the instance of the primary grout bag is between about 600 mm (24 inches) and about 1500 mm (59 inches).
 4. A grout bag assembly as claimed in claim 1 in which the secondary grout bag is located on the top of the primary grout bag.
 5. A grout bag assembly as claimed in claim 1 in which the top of the primary grout bag and the bottom of the secondary grout bag are formed by a single common wall.
 6. A grout bag assembly as claimed in claim 1 in which the primary grout bag and secondary grout bag each have a unidirectional valve-controlled inlet.
 7. A grout bag assembly as claimed in claim 1 in which the primary grout bag and secondary grout bag are secured within a further outer bag.
 8. A grout bag assembly as claimed in claim 1 in which a reinforcing structure is provided about at least the primary grout bag and optionally also the secondary grout bag.
 9. A method of installing a grout bag assembly as claimed in claim 1 comprising positioning the grout bag assembly between a hanging wall and a foot wall of a mine with the bottom of the primary grout bag on the foot wall; filling the primary grout bag by pumping into it a grout to cause it to expand; allowing the grout to set; thereafter filling the secondary bag with grout until the top thereof engages the hanging wall and a required internal pressure is reached within the secondary grout bag; and allowing the grout in the secondary bag to set.
 10. A method of installing a grout bag assembly as claimed in claim 9 in which the grout bag assembly is suspended from its top preparatory to filling the primary grout bag.
 11. A method of installing a grout bag assembly as claimed in claim 9 in which the primary grout bag is filled until such time as the secondary bag in the uninflated condition becomes compressed between the primary bag and hanging wall and inflation of the secondary grout bag is effected to occupy space created between the top of the primary grout bag and the hanging wall by shrinkage of the grout in the primary grout bag. 